Trivia : the display was left "bare" for the japanese and european versions (blue) while the US version had it coloured in amber.

Digital filter is 20bit resolution with 8fs. The digital-to-analogue section is centered around two copper-shielded 20bit dual-balanced converters made by Pioneer - at least the tag says so.
The pre-production units (shown below) had two BurrBrown "PCM63 Proto" converters and completely different audio boards.

The images shown below probably display pre-production board as none of the images I could find here and there shows anything that lavish...
Since the PD-5000 was the first 20bit resolution CD player, there must've been quite a few version of the d/a board. But the same kind of "downscaling" from pre-production to production units happened to the famed PD-95 and probably many others.

An output selector permits to avoid having digital clocks pulsing while only the analogue outputs are used ; display can be switched off, too, for the ultimate in operation silence. Mostly, it'll help save the FL display from ageing too fast.
Although the digital section allowed for it, no analogue balanced output were present : only (big) single-ended RCAs.

In a june 1990 german test review, Sony's CDP-X77ES made it equal to the (prototype) PD-93 : better build-quality for the latter but better sound for the PULSE Sony.
A result later on in clear favor of the subsequent CDP-X777ES and... throughout the rest of the 1990s :)

Pioneer sold a lot of PD-91 and PD-93 in Japan and Europe although not in the same amounts Sony was selling its X7 players...
Both systems were truly excellent at any rate - more a matter of taste in sound and looks.
And both were actually built to play beyond a full decade, if not two - gone-by days, ain't it ?